Supervisors info:
Αριάδνη Αργυράκη Επίκ. Καθηγήτρια (Επιβλέπουσα), Μαρία Οικονόμου Καθηγήτρια , Αθανάσιος Γκοντελίτσας Επίκ. Καθηγητής
Summary:
The aim of this research was to investigate the decrease of mobility of
potentially toxic elements in contaminated soil with the addition of calcined
(350 oC) Greek diasporic bauxite. For that purpose, a pot experiment was set up
where soil, originating from the mining village of Stratoni (Chalkidiki), was
mixed with six different percentages of calcined bauxite: 0%, 1%, 2%, 4%, 5%
and 7%. Bauxite for experimentation was supplied by S&B S.A. After mining the
samples of approximatelly 1 kg each were homogenized and wettet to saturation
by using deionized water. The cycle of wetting and mixing was repeated once a
week over a period of one month. During this period the physicochemical
parameters of amended soil were monitored by measuring pH, TDS and sulfates.
The effectiveness of the process was evaluated at the end of the four weeks by
two leaching tests - EN 12457-4 and Toxicity Characteristic Leaching Procedure
(TCLP). All experiments were carried out in the Laboratory of Economic Geology
and Geochemistry, University of Athens. Concentration of heavy metals and
metaloids was measured in the lechates by ICP-MS in the accredited laboratory
of ACME, Canada (water lechates) and by S&B in a collaborating laboratory in
Germany. In addition, mineralogical characterization (XRD, SEM) and thermal
analysis (TG-DTA) were performed on bauxite samples activated at different
temperatures (105oC, 350oC and 450oC) in order to investigate phase transitions
during the thermal treatment process. Also, a comparison of stabilization
efficiency was carried out for the bauxite material used in the experiment
(350oC) and the same material treated at different temperatures for a given
rate of mixing (7%).
In general, the results of the chemical analyses showed the efficiency of
bauxite (heated at 350oC) and its prospect as a stabilizing factor for
potentially toxic elements in the soil. Particularly, during the two leaching
methods, an improvement in the efficiency of the leachates was observed by
increasing the mixing rate of bauxite (especially for 7% bauxite) for the
elements As, Zn, Ni, Cr, Cu, Cd and Pb whereas the elements Sb, Ba and Mn gave
negative efficiency factors. The low pH of the TCLP reagent reduced the
retention of Zn, Cd, Cu, Cr and Ni in comparison with As, Pb and Sb, while the
elements Ba and Mn were only partially mobilized under acidic conditions. Both
raw and calcined bauxite in a mixing proportion of 7% reduced the leachate
concentration of the elements in comparison to the original soil. Samples that
were mixed with activated bauxite (105 oC, 350 oC) and raw bauxite showed
similar results. The maximum efficiency was observed by using treated bauxite
at the temperature of 450 oC. This difference in retention efficiency of
elements is attributed to phase transitions that occur in Al-oxyhydroxides and
Fe-oxides/oxyhydoxides of bauxite.
Keywords:
Stabilization, Bauxite, Arsenic, Soil, Hydroxylation
